These days, many liquid crystal display devices incorporate a touch panel. For example, the touch panel, which is operable intuitively, is often adopted in liquid crystal display devices incorporated in devices such as a navigation system provided in vehicles.
However, liquid crystal display devices (display devices) incorporating a touch panel suffer problems attributable to touch input. The problems will be described by using a liquid crystal display device 189 shown in FIGS. 5 to 9 (here, FIGS. 6 and 7 are sectional views taken along lines a-a′ and b-b′, respectively, in FIG. 5, and viewed from a direction indicated by arrows in FIG. 5; any member indicated without hatching is shown in side view).
As shown in FIGS. 5 to 7, in the liquid crystal display device 189, a liquid crystal display panel (a display panel) 159 and a backlight unit 149 are accommodated in a box-shaped rear case cs1, and a picture-frame shaped front case cs2 is placed over the liquid crystal display panel 159 accommodated in the rear case cs1. With the two cases cs1 and cs2 fixed to each other, the liquid crystal display panel 159 and the backlight unit 149 are supported between the two cases (herein, the liquid crystal display panel 159, the backlight unit 149, and the two cases cs1 and cs2 holding the liquid crystal display panel 159 and the backlight unit 149 therebetween will together be referred to as a display unit 169). Further, a touch panel 179 is placed over the front case cs2 via a picture-frame shaped cushion sheet 171.
With this arrangement, various problems arise when touch input is performed on the touch panel 179 and thus pressure is applied thereto as shown in FIGS. 8 and 9 which are enlarged sectional views corresponding to FIGS. 6 and 7, respectively. Such problems are caused by transmission of the pressure applied to the touch panel 179, as shown in FIG. 8, to the cushion sheet 171, then to the front case cs2, and further to an internal frame (a frame) fm which serves as the framework of the backlight unit 149.
If pressure is applied to the internal frame fm in this way, the pressure causes partial distortion of the internal frame fm. This results in a phenomenon (pooling phenomenon) in which a display surface of the liquid crystal display panel 159 attached to a support surface fmu of the internal frame fm via a double-stick tape (unillustrated) is adversely affected by the distortion of the internal frame fm and becomes wavy (here, the position of the liquid crystal display panel 159 is regulated by a positioning member fmt which protrudes from the support surface fmu; see FIG. 6). If the pooling phenomenon occurs in this way, it degrades the quality of images displayed on the liquid crystal display device 189.
Further, as shown in FIG. 9, the pressure applied to the touch panel 179 may be transmitted excessively to the front case cs2 via the cushion sheet 171.
Such excessive application of pressure to the front case cs2 makes part of the inner circumference of the picture-frame shaped front case cs2 come into contact with the liquid crystal display panel 159, and this includes the pooling phenomenon in the liquid crystal display panel 159.
A possible solution to the pooling phenomenon described above is, as shown in FIG. 10, to increase the rigidity of the front case cs2 by, for example, increasing a thickness t of the front case cs2 or increasing a width w of one side of the frame. This makes the front case cs2 less likely to warp even when excessive pressure is applied to the front case cs2.
Another possible solution is, as disclosed in Patent Literature 1, to adopt a comparatively large-sized case cs to support the touch panel 179 and to couple the touch panel 179 to the liquid crystal display panel 159 via an adhesive layer 191. With this structure, the case cs is prevented from warping, and furthermore, since the liquid crystal display panel 159 is out of contact with the case cs, the pooling phenomenon attributable to the case cs is less likely to occur in the liquid crystal display panel 159.